The 3rd Generation Partnership Project, 3GPP, is responsible for the standardization of the Universal Mobile Telecommunication System, UMTS, and Long Term Evolution, LTE. The 3GPP work on LTE is also referred to as Evolved Universal Terrestrial Access Network, E-UTRAN. LTE is a technology for realizing high-speed packet-based communication that can reach high data rates both in the downlink and in the uplink, and is thought of as a next generation mobile communication system relative to UMTS. In order to support high data rates, LTE allows for a system bandwidth of 20 MHz, or up to 100 MHz when carrier aggregation is employed. LTE is also able to operate in different frequency bands and can operate in at least Frequency Division Duplex, FDD and Time Division Duplex, TDD, modes.
In 5G, i.e. 5th generation mobile networks, there will be evolvement of the current LTE system to 5G. The main task for 5G is to improve throughput and capacity compared to LTE and to provide support for new services. This is achieved by increasing the sample rate and bandwidth per carrier. 5G is also focusing on use of higher carrier frequencies i.e. above 5-10 GHz.
One main object of a 5G radio concept is to support highly reliable ultra-low delay Machine-Type Communication, MTC, i.e., Critical-MTC. The Critical-MTC concept should address the design trade-offs regarding e.g., end-to-end latency, transmission reliability, system capacity and deployment, and provide solutions for how to design a wireless network for different industrial application use cases. The Critical-MTC system should in particular allow for radio resource management that allows the coexistence between different classes of applications: real time sporadic data, real time periodic data, and best effort traffic. Alert, or alarm messages, is an example of real time sporadic data, that needs to be detected with high accuracy.
Telecommunication networks rely on the use of highly accurate primary reference clocks which are distributed network wide. Telecommunication networks, and in particular systems using time domain multiplexing, generally use some kind of synchronization signals for allowing wireless devices to be in sync with the base station, to which they are connected. Legacy systems, like LTE, uses common synchronization and reference signals. In LTE the common reference signals are transmitted several times every subframe, while synchronization signals are transmitted every 5thsubframe. Thereby, at most within a time period of 5 ms, a synchronization signal can be detected and possible time and frequency error can be adjusted.
Future 5G systems will be based on a lean design where the transmission of broadcast signals like Master information blocks MIB, System information blocks SIB, or similar, and synchronization and reference or pilot signals are only transmitted when necessary, i.e. when they are actually needed for measurements by one or several devices. The main reason for this is to reduce unnecessary interference as well as reduce the radio network node power consumption.
In the 5G system, synchronization signals are dedicated to one or more specific users. Such synchronization signals are referred to as dedicated synchronization signals and are typically only transmitted when and where they are needed. The dedicated synchronization signals are generally transmitted much more seldom than the prior art common synchronization signals. Furthermore, the rate for dedicated synchronization signals may be configurable. Hence, in 5G the wireless devices might not have any reference signals to track for more than e.g. 100 ms.
As mentioned above, in prior art systems, like LTE, the synchronization signal duty cycle 5 ms, and hence for Critical-MTC applications, the sync with the radio network node is not of a problem in the design of high reliable, low latency applications. However in a 5G system having reconfigurable sync and pilot symbol period that might be long, scenarios where sensors transmitting alarm event with irregular long time interval, that need instantaneous detection and reaction once transmitted, might be a problem using prior art approaches.
However, for high reliability detection to be maintained, an accurate and precise synchronization between transmitter and receiver is crucial. This requirement contradicts low synchronization signal rate.